A semiconductor device having a modularized structure of a power switching element such as MOSFET, IGBT or the like and IC for driving the power switching element (also called as power module) has been hitherto known as a semi conduct or device used for power conversion of an inverter or the like. In this type of semiconductor device, an insulating board having a power switching element mounted therein and a control board having IC which is mounted therein and controls the power switching element are arranged and modular ly configured in the same housing.
Recently, advancement in performance of power switching elements has promoted increase of current flowing through the power switching elements and increase of the switching speed thereof. However, magnetic field having a large magnetic field intensity occurs when a power switching element is switched, and there has been a problem that this magnetic field causes malfunction of IC on the control board and various kinds of circuits.
Specifically, a GND (GND; Ground) pattern is provided on the control hoard to reserve ground potential (hereinafter referred, to as GND potential), and GND pins are arranged at both the sides of IC so as to confront one another so that each GND pin is connected to the GND pattern when IC is mounted. The GND pins at both the sides of IC are electrically connected to one another in internal circuits of IC. Therefore, when the IC is provided on the GND pattern, a GND loop through which the internal circuits of IC, the GND pins at both the sides of the IC and the GND pattern are connected to one another is formed. When this GND loop crosses magnetic field occurring at the switching time of the power switching element, induction current is induced in the GND loop and therefore the GND potential varies, so that malfunction of IC and the various kinds of circuits may occur.
Therefore, there has been proposed a technique of arranging a plane containing a GND loop in a control board substantially vertically to the direction of main current flowing in an insulating board in which a power switching element is mounted, thereby preventing magnetic field caused by the main current from generating induction current in the GND loop (see Patent Document 1, for example).